§ 100. THE CHEMICAL ANALYSIS. 177 



silicic acid dissolved in the two cases furnishes a means 

 of estimating the extent of the action of the cold acid on 

 the silicates in the soil. 

 Treatment of the Soil with Carbonated Water. 

 100. To determine only the total quantity of organic 

 and inorganic matters in the soil, soluble in water con- 

 taining carbonic acid in solution, without reference to the 

 composition of the dissolved substances, put 500 gnns. 

 of air-dried soil in a flask that can be well stoppered, and 

 l^our over it as much carbonated water as will make, to- 

 gether w^ith the hygroscopic water in the soil, 2000 c.c. 

 The water should be ^|^ saturated w^ith carbonic acid, by 

 saturating 500 c.c. at the common temj^erature and press- 

 ure, and mixing this Avith 1500 c.c. of pure water. When 

 thus prepared, the water is more nearly like that in the 

 soil, whose action we wish to imitate. 



Leave the soil and water in contact with each other 

 three days, with frequent agitation, then j^our off 1000 

 c.c. of as clear a liquid as possible, representing 250 grms. 

 of soil, and filter through a double filter, while keej^ing 

 the funnel well covered with a glass plate. Evaporate 

 the clear filtrate to dryness at a temperature below boil- 

 ing, dry the residue at 125° C, weigh, ignite, and after 

 treatment several times with ammonic carbonate and 

 gentle ignition, weigh again. The difference between the 

 two weights gives the amount of organic matter dissolved 

 by the carbonated w^ater. 



The carbonic acid is determined in the ignited residue, 

 as in § 60. 



If a detailed chemical examination of the solution in 

 carbonated water is to be made, at least 1500 grms. of 

 soil must be taken instead of 500, and the water in the 

 same proportion. After three days, pour oif 4000 c.c. of 

 the clear supernatant liquid, representing two-thirds of 

 the soil, let it stand 24 hours in well-closed and full 

 bottles, filter as directed above, and without disturbing 

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